1. Field of the Invention
This invention relates to certain organic, silver halide complexing agents and photographic elements, compositions and processes for diffusion transfer systems. In one of its aspects the invention relates to a photographic product for a diffusion transfer system which employs certain organic, silver halide complexing agents. Another aspect of the invention relates to a photographic processing composition comprising a silver halide developing agent with such organic, silver halide complexing agents. A further aspect relates to a photographic process for a diffusion transfer system employing the described silver halide complexing agents.
2. Description of the State of the Art
Photographic diffusion transfer processes, compositions and elements have become well known in recent years. A diffusion transfer system is characterized by the use of a photographic element, typically containing a photographic silver salt, and an image receiver or precipitating layer contiguous to the photographic silver salt. After exposure of the photographic element, typically a processing composition, such as one containing a silver halide developing agent and a silver halide complexing agent, is applied between the exposed photographic element and the image receiver or precipitating layer. The processing composition, in practice, has contained a silver halide solvent, such as sodium thiosulfate, which causes the unexposed silver salt, usually silver halide, to dissolve, forming a silver complex which diffuses to the image receiver or precipitating layer where development nuclei or an image precipitating agent in that layer causes the silver to be reduced or precipitated from the silver complex imagewise. Development nuclei or precipitating agents can be present in the image receiver before contact with the complex silver or the nuclei can be formed in situ. Typical diffusion transfer systems, elements, compositions and processes are described, for example, in U.S. Pat. No. 2,698,237 of Land issued Dec. 28, 1954; U.S. Pat. No. 2,647,056 of Land issued July 28, 1953; and U.S. Pat. No. 3,345,166 of Land issued Oct. 3, 1967.
A processing composition employed in a typical diffusion transfer system normally contains a silver halide developing agent and a silver halide complexing agent. Processing is usually carried out by applying a viscous fluid layer between the photographic element and an image receiving layer as described.
The requirements for silver halide developing agents and silver halide complexing agents for diffusion transfer systems are very stringent and relatively few such agents which are satisfactory for general silver halide developing processes are satisfactory or sufficiently active for diffusion transfer systems without providing undesired sensitometric properties. Attempts have been made to provide a replacement for thiosulfate silver halide complexing agents which provides the desired silver complex and image transfer. Thiosulfate silver halide complexing agent replacements are described, for example, in U.S. Pat. No. 2,857,274 of Land et al. issued Oct. 21, 1958; U.S. Pat. No. 2,857,275 of Land et al. issued Oct. 21, 1958 and U.S. Pat. No. 2,857,276 of Land et al. issued Oct. 21, 1958. Uracil is a typical compound which has been employed in combination with, for example, a nitrogenous base to replace a thiosulfate silver halide complexing agent in a diffusion transfer system.
There has accordingly been a counting need to provide organic, silver halide complexing agents for diffusion transfer systems, elements, compositions and diffusion transfer processes which provide desired maximum density. There has also been a continuing need to provide an organic, silver halide complexing agent which provides desired silver halide complexing activity in processing composition which hydroxylamine silver halide developing agents. There has been a further need to provide a suitable organic, silver halide complexing agent which is a replacement for thiosulfate silver halide complexing agents and which provides a desired image in a diffusion transfer system.